1. Technical Field
The present invention relates to a photoconductive antenna, a terahertz wave generating device, a camera, an imaging device, and a measuring device.
2. Related Art
In recent years, attention has been devoted to terahertz waves, which are electromagnetic waves with frequencies of 100 GHz or greater and 30 THz or less. Terahertz waves can be used in various forms of measurement and non-destructive testing such as imaging and spectrometry.
The terahertz wave generating device that generates these terahertz waves has a light source device that generates light pulses (pulsed light) having pulse widths at the approximately sub picosecond level (several hundred femtoseconds) and a photoconductive antenna that generates terahertz waves by irradiating light pulses generated by the light pulse generator.
As the photoconductive antenna, for example, disclosed in Japanese Laid-Open Patent Application Publication No. 2007-300022 is a terahertz wave generating device (photoconductive antenna) having a laminated body (pin structure) for which an n type semiconductor layer, an i type semiconductor layer, and a p type semiconductor layer are laminated in that order. With this photoconductive antenna, when light pulses are irradiated on the p type semiconductor layer via an aperture formed on an electrode provided on the p type semiconductor layer, terahertz waves are emitted radially from the entire side surface of the i type semiconductor layer.
With the photoconductive antenna noted in the above mentioned publication, for a dipole shaped photoconductive antenna (PCA) using a low temperature growth GaAs (LT-GaAs) substrate, it is possible to make the intensity of the generated terahertz waves approximately 10 times larger.
However, with the photoconductive antenna noted in the above mentioned publication, light pulses are irradiated on the p type semiconductor layer, and the light pulses that pass through that p type semiconductor layer are made incident on the i type semiconductor layer, so a portion of the light pulses are absorbed by the p type semiconductor layer, and because of that, there is the problem that the terahertz wave generating efficiency decreases.